JPH0327885B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a transmission screen with a Fresnel lens used as a rear projection screen or the like. [Prior Art] A rear projection screen is used as a screen for a video projector, a microfilm reader, etc., and a circular Fresnel lens sheet is often used to provide a light condensing effect. By the way, this kind of Fresnel lens is
For example, it has transmission characteristics as shown in FIG. That is, such a Fresnel lens is configured such that a large number of prisms 10 having a triangular cross section are arranged, and the prisms 10 are arranged on the lens surface 1.
1 and a non-lens surface 12. If the Fresnel lens surface of this Fresnel lens is used as the entrance surface X, the incident light will be emitted to the exit surface Y as shown in the figure. At this time, the light L incident on the lens surface 11
is refracted and emitted toward the exit surface Y side as effective light, but the light L' incident on the non-lens surface 12 does not contribute to the condensing effect. This tendency becomes more severe as the light source approaches the screen at a location further away from the light source or even at the same location, and in such a case, the amount of light incident on the non-lens surface 12 of the prism 10 increases. Furthermore, in such a case, since the angle of incidence of the light beam entering the prism 10 increases, the amount of transmitted light also decreases due to surface reflection, making it increasingly difficult to expect an effective amount of light. This surface reflectance can be determined using Fresnel's equation, which is expressed by the following equation. Surface reflectance (R) = 1/1 {tan ² (i-γ)/tan ² (i + γ) + sin ²
(i−γ)/sin ² (i+γ)} Here, i is the incident angle and γ is the refraction angle.
For example, if the material of the Fresnel lens is acrylic resin (refractive index n=1.49), the following holds true: sin i/sin γ=n where n is the refractive index. The surface reflectance can be calculated from the above formula. For example, when the angle of incidence is 70°, the surface reflectance is 15%, and when the angle of incidence is 80°, it is 40%, and this amount of loss is caused by surface reflection alone. Based on this calculation, assuming that the distance from the light source is 1000 mm and the convergence distance of the Fresnel lens is f = 1000 mm or less, most of the incident light is I know that I will end up losing money. Recently, there has been a movement to make this type of screen even larger, and there is also an opportunity to reduce the depth of the device, so the above-mentioned loss of light amount has come to be seen as a problem. For this reason, the applicant has already proposed a Fresnel lens equipped with a prism piece at the periphery so that a portion of the light rays incident on one lens surface is totally reflected on another lens surface and then emitted. (Special Application No. 57-227909). FIG. 5 shows the prism piece in this case. The prism piece 20 has two lens surfaces 21 and 22, and part of the light incident on one lens surface 21 is transmitted to the other lens surface. 22, the light is totally reflected and emitted. In this way, the amount of light is lost in the area where the angle of incidence on the Fresnel lens sheet is large (L' ray)
has the advantage of being smaller than the Fresnel lens shown in FIG. Therefore, when the projection distance to the Fresnel lens sheet is short, that is, when the angle of incidence is large, the light can be emitted to the viewing side with less loss than in the conventional case. [Problem to be solved by the invention] However, in a prism piece having a total reflection surface 22 as shown in FIG.
1, it is emitted to the observation side without hitting the total reflection surface 22, and becomes a luminous flux L''. This luminous flux L'' causes rainbow patterns, color separation, and pieciade on the screen, and changes the image on the screen. There were problems that degraded the quality. [Means for Solving the Problems] An object of the present invention is to solve the above-mentioned problems and provide a good transmission screen that does not cause rainbow patterns or the like. The purpose of the above is to provide a transmissive screen with a Fresnel lens that uses a Fresnel lens surface as a light-receiving surface, in which at least a portion of the prism pieces constituting the light-receiving surface is such that a portion of the light beam incident on the incident surface faces the It has a total reflection surface that is totally reflected and exits to the observation side, and a means for preventing light from going straight is provided on the part of the entrance surface where the light beam that does not hit the total reflection surface is incident. This is achieved using a transmission screen with a Fresnel lens featuring the following features:
[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings. FIG. 1 shows a first embodiment of the present transmission type screen, and is an enlarged view of a Fresnel lens piece. In the figure, 1 is an entrance surface, and 2 is a total reflection surface that reflects the light from the entrance surface 1 and outputs it to the observation side. The entrance surface 1 has a surface 3 (of course, only B may be used) that is roughened to a portion B that receives the light beam L' that does not hit the total reflection surface 2 and a portion C that does not receive light. Due to diffusion, the light flux L'' that causes rainbows etc. is not generated. In order to manufacture the Fresnel lens sheet having the prism pieces of this first embodiment, the above-mentioned portions are made of roughened gold. It can be easily manufactured by making a mold and thermally transferring it. Figure 2 shows the second embodiment of this transmission type screen, and is an enlarged view of a Fresnel lens piece. In the figure, 1 is the entrance surface, and 2 is the entrance surface. A total reflection surface, 4 a diffusing agent, and 5 a low refractive index material layer.In this example,
By forming a light diffusing layer 6 with the diffusing agent 4 and the low refractive index substance 5, and forming the light diffusing layer 6 so as to cover the portion B that receives the light beam L' that does not enter the total reflection surface 2, the incident light is L' is diffused and the negative effect on the image is suppressed. Although the incident light L is reflected by the total reflection surface 2 due to the presence of the low refractive index substance 5, it is preferable that the diffusing agent 4 does not come into contact with the total reflection surface 2 so as not to interfere with the total reflection function. Further, the diffusing agent 4 is preferably located on the surface of the light diffusing layer 6 in order to efficiently diffuse the incident light L'. In order to position the diffusing agent 4 on the layer surface, first coat the low refractive index substance 5 on the total reflection surface 2, and then apply a coating liquid containing the diffusing agent (it is not necessary to separately add the low refractive index substance 5). ), and another method uses the difference in specific gravity between the diffusing agent 4 and the low refractive index substance 5 to position the diffusing agent 4 on the surface of the layer. The method for manufacturing this transmission screen is to create a Fresnel lens and then create the light diffusion layer 6 in post-processing. It is convenient if the light diffusion layer 6 is formed in the form of a roll by pressing the paint into it, since almost no paint will remain on the top part of the prism (corresponding to the above-mentioned part A). FIG. 3 shows a third embodiment of the present transmission type screen, and is an enlarged view of a Fresnel lens piece. In the figure, 1 is an incident surface, 2 is a total reflection surface, 5 is a low refractive index material, and 7 is a light absorbing material. In this embodiment, after the low refractive index material 5 is applied, the light absorbing material 7 is applied thereon. In this way, the light beam L' that does not enter the total reflection surface 2 is absorbed by the light-absorbing substance 7, and the adverse effects of the incident light L' are eliminated. Furthermore, since the layer of low refractive index material 5 provided on the total reflection surface 2 is located between the light absorbing materials 7, the total reflection function is not inhibited. Similarly to the second embodiment, the coating method of this embodiment can be easily manufactured by pushing the paint into the coating using a roll. Further, the transmission type screen of the present invention has a first, a second,
The present invention is not limited to the one shown in the third embodiment, and various embodiments can be adopted depending on the purpose of use. For example, it can be applied to the rear projection screen of Japanese Patent Application No. 119340/1983, which has prisms with total reflection surfaces on the periphery, and prism pieces with refractive surfaces and prism pieces with total reflection surfaces are alternately combined. The present invention can also be applied to the transmission type screen disclosed in Japanese Patent Application No. 174347/1982 and the transmission type screen disclosed in Japanese Patent Application No. 158328/1982, which is an improved version of the invention. In addition, the incident angle of a prism piece with a total reflection surface changes depending on the position on the screen.
It can also be applied to transmission screens using the Fresnel lens of No. 149224. However, the surface roughening method of the first embodiment can also be applied to a screen in which prism pieces having a refractive surface and prism pieces having a total reflection surface are alternately combined; This method can only be used in areas where total reflection prism pieces are continuous. This is because the coating liquid adheres to the refractive surface of the prism piece having a refractive surface and prevents light from entering from the refractive surface. Next, a specific method for manufacturing the total reflection Fresnel lens of the transmission type screen of the present invention will be described. (Example 1) As described in the first example, the first
The total reflection Fresnel lens of the first example was obtained by thermally transferring methyl methacrylate to a mold whose surface was roughened in the areas shown in FIGS. B and C. (Example 2) P (pitch) = 0.5, refractive index n = 1.39, plate thickness 3 mm
Prepare a total reflection Fresnel lens with 20% vinylidene fluoride and 60% methisobutyl ketone (MIBK).
%, methyl ethyl ketone (MEK) 20% paint,
Alumina oxide Al ₂ O ₃ was added at 1/100 as a diffusing agent and mixed uniformly and coated with a roll coater to obtain a total reflection Fresnel lens of the second example. (Example 3) P (pitch) = 0.5, refractive index n = 1.39, plate thickness 3 mm
A total reflection Fresnel lens was prepared, and paint containing 20% vinylidene fluoride, 60% MIBK, and 20% MEK was applied using a roll coater. After drying, enamel black (Musashi Paint Plaace 716) was applied using a roll coater. In this way, a total reflection Fresnel lens of the third example was obtained, in which a light absorption layer was formed at the bottom of the valley between the prisms. The total reflection Fresnel lenses of the first, second, and third examples obtained as described above have constant diffusion characteristics (screen peak gain approximately 20 to 30, diffusion angle characteristic β = ±
A screen was made by combining a light-transmitting diffuser plate with an angle of 10°), and a visual evaluation was performed between a conventional total reflection Fresnel lens and a screen using the above-mentioned diffuser plate. The results are summarized in Table 1.

〔Effect of the invention〕

As can be seen from Table 1, the transmissive screen of the present invention was able to provide a good transmissive screen that was free from streaks and blurred images compared to conventional transmissive screens.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 show first, second, and third embodiments of the transmission screen of the present invention, respectively, and are enlarged views of Fresnel lens pieces. FIG. 4 is a schematic diagram showing a conventional refractive Fresnel lens, and FIG. 5 is a schematic diagram showing a conventional total reflection Fresnel lens. 1...Incidence surface, 2...Total reflection surface, 3...Rough surface,
4... Diffusion agent, 5... Low refractive index material, 6... Light diffusing layer, 7... Light absorbing material.

Claims (1)

[Scope of Claims] 1. A transmissive screen with a Fresnel lens that uses a Fresnel lens surface as a light-receiving surface, wherein at least a portion of a prism piece constituting the light-receiving surface is such that a portion of the light beam incident on the incident surface faces the It has a total reflection surface that completely reflects the light and emits it to the observation side.
Moreover, a transmission type screen with a Fresnel lens is characterized in that a portion of the incident surface on which the light flux that does not hit the total reflection surface is incident is provided with means for preventing light from going straight. 2. A transmitting device with a Fresnel lens according to claim 1, wherein the means for preventing light from going straight is carried out by roughening a portion of the incident surface and diffusing the incident light on that portion. type screen. 3. The Fresnel lens according to claim 1, wherein the means for preventing light from going straight is carried out by diffusing the incident light at that portion using a low refractive index material layer mixed with a diffusing agent. Comes with a transparent screen. 4. According to claim 1, the means for preventing light from going straight is carried out by absorbing incident light in that portion by a light absorption layer formed on the low refractive index material layer. Transparent screen with Fresnel lens.